RU2395538C2 - Improved foamed materials for absorbing energy of vehicle - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to polymer foamed materials which absorb energy when a vehicle collides with obstacles, such as other vehicles. In particular, the invention pertains to an energy absorbing structural component which contains an amorphous thermoplastic cellular polymer which is a polystyrene polymer or a polystyrene copolymer which is in contact with the structural component, in which at least approximately 50% of the cells of the amorphous cellular polymer are closed and have average gas pressure between approximately 0.5 atm and approximately 1.4 atm at ambient temperature. The invention also relates to a method of making the energy absorbing structural component, involving: (a) mixing the amorphous thermoplastic polymer, which is a polystyrene polymer or polystyrene copolymer, and a foaming agent, (b) preparation of moulded polymer foamed material from the mixture of the polymer, which is a polystyrene polymer or polystyrene copolymer, and the foaming agent, in which the foamed material has at least approximately 50% closed cells, (c) processing the moulded foamed material such that closed cells have gas pressure between approximately 0.5 atm and approximately 1.4 atm in order to obtain processed moulded foamed material, and (d) attaching the processed moulded foamed material to the structural component to obtain an energy absorbing structural component.

EFFECT: obtaining foamed materials which absorb energy of a vehicle, which are cheap, are lightweight, have high energy absorption and can withstand the internal medium of an automobile.

43 cl, 5 ex, 1 tbl, 2 dwg

Description

Cross reference to a "related" application

This application claims the rights of provisional application US Provisional Application No. 60757582, registered January 10, 2006, which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to polymeric foam materials absorbing energy in a collision with an obstacle of vehicles, such as automobiles.

The scope of the invention

Foamed polymers are widely used in a variety of shock absorbing devices. Foams are commonly used in pillows, seats, mattresses and similar devices, where softness and comfort are the predominant factors. Foams are also used to cushion the contents of the box. In packages, the foam usually only softens the impact due to collision or falling of the package and as a result, it only elastically deforms (i.e., the foam after deformation returns to its shape, which is usually about 10% less than before deformation). Packaging foam also has few, if any, requirements regarding the size of the foam, it only has to absorb the contents against weak impacts. Therefore, all this is quite common for inexpensive loose polystyrene and loose pulp, which are the basis for the packaging material in the form of small nuts, used even if each of them is subject to significant deformation due to temperature and humidity, respectively.

In recent years, increasingly stringent requirements have been placed on automobiles to reduce bodily injury to a passenger during an accident. To achieve this, airbags from frontal collisions were placed in cars. More recently, more and more attention began to be paid to side collisions with an obstacle and head injuries when turning the car over. This required the use of side airbags and laid the foundation for the use of foam, which absorbs energy not only in case of elastic deformation, but also in inelastic deformation (i.e., in a collision).

The vast majority of foams used to mitigate automobile collisions were foamed thermoplastics with closed crystal cells, such as foamed polypropylene balls and propylene coalescing foamed tape (e.g. STRANDFOAM, a trademark of The Dow Chemical Company). Each of these automotive energy-absorbing foams tends to be expensive and have more weight for absorbed compressive energy than we would like. However, due to their existence, for example, in crystalline or thermoset form, they exhibit excellent dimensional stability, which is required by automakers to guarantee adequate energy absorption during a collision, as well as the prevention of any creaking, noise or rattling during movement.

Other polymeric foam materials, such as polystyrene foam materials, which are common in packaging, as described previously, have tried, but have not achieved much, in commercial acceptability, mainly because of their insufficient dimensional stability in a harsh environment in which is a car. For example, the inside of a car can be affected by temperatures from minus 20 ° C or lower in winter, such as in Alaska, to temperatures approaching 100 ° C due to the sun in the death valley (you can easily boil an egg on the top of the car's roof).

Therefore, it would be desirable to provide foams that absorb energy from a vehicle that are inexpensive, lightweight, good energy absorption, and can withstand the car’s internal environment.

SUMMARY OF THE INVENTION

A first aspect of the invention is a unit comprising an amorphous thermoplastic cellular polymer in contact with a structural element, wherein at least 50% of the cells of the amorphous cellular polymer are closed cells, and the closed cells have a gas pressure that is from about 0.5 atmosphere to about 1.4 atmospheres at ambient temperature (i.e. approximately 23 ° C).

Surprisingly, it was found that amorphous foamed material, when it has the aforementioned pressure in the cell, even though it may have a low transition temperature from a highly elastic state to a glassy state (e.g., polystyrene), can be introduced into the structural component of the transport means, such as a door, to form a structural element that absorbs energy without significant deformation (for example, satisfies automotive dimensional stability specifications).

The second aspect of the invention is a method for producing a unit link absorbing energy, including:

(a) mixing an amorphous thermoplastic polymer and a blowing agent,

(b) the formation of the formed polymer foamed material from a mixture of a polymer and a foaming agent, where the foamed material contains at least 50% of closed cells,

(c) treating the formed formed foam material, such as closed cells having a gas pressure of from about 0.5 to about 1.4 atmospheres, to create a processed, formed, foam material, and

(e) attaching the processed, formed foam material to the structural element to obtain an energy absorbing structural element.

The method can be used to create a structural element absorbing energy in vehicles, such as cars, buses, trucks, trains, airplanes, motorcycle helmets, emergency barriers and any other means of transportation where energy absorption from a strong impact would be implemented.

A third aspect of the invention is an energy absorbing structure element that includes an amorphous thermoplastic cellular polymer in contact with a structural element, wherein at least about 50% of the amorphous cellular polymer cells are closed cells and the closed cells have a blowing agent containing carbon dioxide. Surprisingly, when CO ₂ is the primary blowing agent, it has been found that the dimensional stability of the energy absorbing structural member is significantly improved compared to other blowing agents.

A fourth aspect of the invention is an element of an energy-absorbing structure that includes an amorphous thermoplastic cellular polymer in contact with a structural element, where at least about 50% of the cells of the amorphous cellular polymer are closed cells and the thermoplastic cellular polymer is perforated so that the maximum distance between the holes is not more than about 60 mm. Unexpectedly, it was also found that the use of perforation in the foam material of the structural element, absorbing energy, manifests itself in excellent stability in size.

Brief Description of the Drawings

Figure 1 is a photograph of a block of polystyrene foam that has been perforated (right block), in comparison with a block made of the same polystyrene foam, but without perforation (left block), a left block that does not have inside the cell pressure necessary for of this energy absorbing structural member of the present invention.

Figure 2 is a graph of the maximum change in linear size depending on the effects on foamed materials heated to 85 ° C, for various influences that are used to empirically determine the average internal pressure inside the cells of the foamed material.

DETAILED DESCRIPTION OF THE INVENTION

Energy Absorbing Element

The invention is an element of an energy-absorbing structure, including an amorphous thermoplastic cellular polymer in contact with a structural element. A structural element of an energy-absorbing structure element is any system that supports or acts in conjunction with a cellular polymer (referred to herein as “foam material”) to distribute exposure energy, such as a car accident. Examples of structural elements are vehicle door panels, beams, dashboards and roofs; helmet shells; road barriers. Preferably, the structural element is a door panel, a door pillar, an instrument panel or a roof of a car or truck. It is understood that the structural element of the structure is necessary to retain or act as support for the cellular polymer, and it is not intended that the structural element of the structure is a component that is necessary for a larger device (e.g., a car), even though it may be.

The energy absorbing structure element also includes an amorphous thermoplastic cellular polymer. “Amorphous” means, as a general concept in technology, the absence of a specific crystalline structure, as well as a specific melting point. Nevertheless, there may be some very poorly ordered structures, but due to the magnitude of such ordering, the technique of measuring ordering, for example, cannot distinguish or does not significantly distinguish them from amorphous material. For example, the ordered interval can be so small that the x-ray diffraction will give, as a result, such a wide spread that if such an interval were presented, it would be no more than about 50 to 100 nanometers in size. Even though the polymer is amorphous, a small portion may show some localized size structures, such as a cell that defines the melting point but is not present. Visually, the X-ray diffraction grating can show small peaks that can be recognized in the noise of the X-ray technique.

By polymer is meant a synthetic organic polymer or possibly any other suitable thermoplastic amorphous polymer. Typical, suitable polymers include polystyrene and polystyrene copolymers. Polystyrene means a polymer of styrene monomer derived from styrene monomer (e.g. substituted styrene), or combinations thereof. Examples of substituted styrenes are o- methylstyrene, m -methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, p-tert-butylstyrene, p-chlorostyrene. Preferably, the polystyrene polymer is polystyrene.

Polystyrene copolymer means a copolymer of styrene monomer (styrene and derivatives of styrene monomer) as previously described and a copolymer that is not a styrene monomer. Typical monomers introduced for the synthesis of the copolymer include acrylonitrile, poly (2,6-dimethyl-1,4-diphenyl ether), methyl acrylate, methacrylonitrile, maleimide, acrylic acid, methacrylic acid, maleic anhydride, itaconic anhydride, or combinations thereof. Preferably, the monomers introduced for the synthesis of the copolymer are acrylonitrile, maleic anhydride, or combinations thereof. A more preferred monomer introduced for the synthesis of the copolymer is acrylonitrile.

Basically, the amount of polystyrene monomer in the polystyrene copolymer is at least about 50% per mole of copolymer. Typically, the amount of monomer introduced for the synthesis of the copolymer is from about 1% to 50% per mole of polystyrene copolymer. Preferably, the amount of monomer introduced for the synthesis of the copolymer is at least 5%, more preferably at least about 10%, even more preferably at least about 20%, and most preferably at least about 25% per mole of polystyrene copolymer.

A preferred polystyrene copolymer is a styrene acrylonitrile copolymer (SAN). SAN copolymer may have from 1% to 50% by weight of acrylonitrile. Preferably, acrylonitrile is present in an amount of from at least about 5%, more preferably from at least 10%, and more preferably from at least about 15%, to preferably not more than 40%, more preferably not more than about 35%, and most preferably not more than about 30% by weight of the SAN copolymer.

The polymer may be of any useful weight, ordinary molecular weight (Mw). Illustratively, the Mw of the polystyrene or polystyrene copolymer can be from 10,000 to 1,000,000. Preferably, the Mw of the polystyrene or polystyrene copolymer is not less than 80,000, more preferably not less than about 100,000, and most preferably not less than about 150,000, more preferably not more than about 400,000, more preferably to not more than about 350,000, and most preferably to not more than about 300,000.

The molecular weight distribution of Mw / Mn can be any suitable distribution, which will at least partially depend on the use of the individual polymer and be easily corrected by experience in technology. Illustratively, the molecular weight distribution of the Mw / Mn polystyrene or polystyrene copolymer is preferably from not less than about 1.0, more preferably from not less than about 1.5, and most preferably from not less than about 2.0, to preferably not more than about 10.0, more preferably up to not more than about 7.0; and most preferably up to not more than about 4.0.

In addition, the polymer may also contain other additives as long as it remains an amorphous thermoplastic polymer. Examples of other additives include small amounts of crosslinking agents (e.g. divinylbenzene), colorants, UV protectants, antioxidants, fillers, flame retardants, antistatic agents, nucleation control agents and the like.

The polymer in the element of the energy-absorbing structure is cellular. Cellular (foam) generally has a clear meaning in the field in which the polymer has an apparent, substantially reduced density, including cells that are either open or closed. A closed cell means that the gas inside this cell is isolated from the gas of another cell by the polymer walls forming the cell. An open cell means that the gas in this cell is not limited in space and can flow into the atmosphere without passing through other polymer cells.

At least about 50% of the foam cells are closed. It is important to have this number of closed cells, because in the process of crushing, these cells can contribute to energy absorption when the structural element absorbing energy becomes squeezed. Also, closed cells can participate to a greater extent in the dissipation of the impact energy, it was discovered that a small number of open cells is desirable when the corresponding average gas pressure is achieved, which is necessary to achieve the acceptable dimensional stability that is required with the foam used, for example, in the upper plates of vehicles . The indicative standard for this is the GMN8351 standard of General Motors. This standard requires that cube-shaped foam with a side of 50 mm be exposed three times to the impacts shown in table 1, and despite this, it does not change in any dimension by more than 3% after these impacts.

Table 1 72 hours at 85 ° C 24 hours when exposed to temperature and humidity 8 hours at -30 ° C 40 hours at 85 ° C 24 hours when exposed to temperature and humidity 8 hours at -30 ° C

Preferably, for the above reasons, at least about 55%, more preferably at least about 60% and more preferably at least about 75% and most preferably at least about 90% of the foam cells are closed cells.

In a preferred embodiment, all open cells of the foam are located on the surface of the foam in one or more shells defining a cavity within the foam or a combination thereof. Such open cells can be obtained, for example, when planning the surface of the foam or perforating the foam with a punch, which is described in more detail below. For foam, it is especially desirable to have a maximum distance from the closed cell to disperse the gas into the atmosphere, but not more than about 60 mm. The maximum gas scattering distance is the linear distance that a molecule or gas atom must travel to reach the atmosphere surrounding the foam, and includes the ability to reach an open cell, such as an open cell inside the foam perforation space. Preferably, the maximum gas dispersion distance is not more than about 50 mm, more preferably not more than about 30 mm, even more preferably not more than about 20 mm, and most preferably not more than about 15 mm.

It is also desirable that the foam in the energy absorbing structural member has the lowest possible density providing sufficient energy absorption, which is usually a function of the expected specific effect. In structural elements that absorb impacts that are designed to mitigate head damage, such as opposed top pads, helmets, and the like, the cellular polymer also favorably exhibits compressive strength, in the direction of the expected impact, of at least 250 kPa, preferably at least 290 kPa, at a voltage of 25% - up to about 700 kPa, especially up to about 600 kPa, as measured by 25-50 mm in the thickness of the sample, with a strain rate of 0.08 s ^-1 .

For these devices, the cellular polymer preferably has a density of not more than about 3.5 lb / ft ³ (56 kg / m ³ ), preferably not more than about 2.5 lb / ft ³ (40 kg / m ³ ), more preferably not more than about 2.35 lb / ft ³ (37.6 kg / m ³ ). A density of at least about 1.5 lb / ft ³ (24 kg / m ³ ) is preferred. A particularly preferred density is from about 1.75 to about 2.2 lb / ft ³ (28-35.2 kg / m ³ ). It has been found that a cellular polymer having such compressive strength and density values tends to have particularly low HIC (d) values measured in accordance with FMVSS 201 (U). Cellular polymer is especially preferred for use in cases of head damage, when the tested compressive strength at 25% is 290-600 kPa, density is from 1.5 to 2.2 lbs / ft ³ (24-35 , 2 kg / m ³ ) and a flexible stress limit - from 3-10%.

For devices that reduce impact and protect the pelvis from damage, such as a shock absorbing pad for the pelvis and something similar, the cellular polymer also exhibits compressive strength, in the direction of the expected impact, with a force of at least 250 kPa, mainly from at least 350 kPa at 25% voltage up to about 1000 kPa, especially up to about 900 kPa, measured at 25-50 mm in thickness of the sample, at a voltage level of 0.08 s ^-1 . For these impacts, the cellular polymer preferably has a density of not more than 5 lb / ft ³ (80 kg / m ³ ) and preferably not more than 4.5 lb / ft ³ (72 kg / m ³ ). A density of at least 2.0 lb / ft ³ (32 kg / m ³ ) is preferred. A particularly preferred density is from about 2.1 to about 4.0 lb / ft ³ (34-64 kg / m ³ ). These denser cellular polymers still tend to exhibit the desired, almost constant, compressive stress, above a wide area of plastic deformation. A particularly preferred cellular polymer for use in devices for protecting the pelvis from damage will have, as noted in tests previously, compressive strength at 25% residual deformation and a force of 300-900 kPa, density 2.1 to 4.0 lbs / ft ³ (34-64 kg / m ³ ) and an elastic limit of 3-10% of permanent deformation. In devices for attenuating effects on the chest, such as a buffer for the chest and the like, the cellular polymer also predominantly exhibits compressive strength in the direction of the expected impact of at least 150 kPa, preferably from at least 200 kPa, with 25% residual deformation up to about 700 kPa, especially up to about 500 kPa, measured 25-50 mm in thickness of the sample at a strain rate of 0.08 s ^-1 . For these devices, the cellular polymer preferably has a density of not more than 3.0 lb / ft ³ (48 kg / m ³ ), preferably not more than 2.0 lb / ft ³ (32 kg / m ³ ). A preferred density is at least 1.25 lb / ft ³ (20 kg / m ³ ). A density of from about 1.5 to about 2.0 lb / ft ³ (24-32 kg / m ³ ) is particularly preferred. These more flexible cellular polymers still tend to exhibit the desired, almost constant, compressive stress, above a wide area of plastic deformation. A particularly preferred cellular polymer for use in devices for protecting the pelvis from damage will have, as noted in tests previously, compressive strength at 25% residual deformation of 200-500 kPa, density from 1.5 to 2.0 lbs / ft ³ ( 34-64 kg / m ³ ) and the elastic limit of 3-10% of permanent deformation.

Further, the cellular polymer predominantly exhibits a compressive efficiency of at least 70% and preferably at least 80% at 60% residual deformation, at least 60% and preferably at least 75% at 65% residual deformation, at least 55% and preferably at least 70% at 70% of permanent deformation and / or not less than 50% and preferably not less than 65% at 75% of permanent deformation. Compressive efficiencies of 85% or more can be obtained in accordance with the invention at 60-65% residual deformation. The compressive efficiency is calculated by compressing the foam at a strain rate of 0.08 s ^-1 by the method described previously, and simultaneously recording the load and the resulting strain. The resulting stress is calculated by distributing the simultaneous load over the initial cross-sectional area of the foam sample in the compression direction. Temporarily occurring deformation is calculated by dividing the change in thickness by the original thickness. The compressive efficiency is then calculated using the ratio

Where σ represents the instantaneous stress, usually in MPa, ε represents the resulting strain and σ _max represents the maximum stress achieved at the same node as the instantaneous stress.

Cellular polymer cells can have an average size (largest size) of from about 0.05 to about 5.0 mm, especially from about 0.1 to about 3.0 mm, as measured by ASTM D-3576-98. Cellular polymers having large average mesh sizes, in particular from about 1.0 to about 3.0 mm, or from about 1.0 to about 2.0 mm, are of particular interest in the largest dimension. It has been found that cellular polymers, often having increased mesh sizes, have better compressive efficiency at high levels of permanent deformation. The sizes of the smallest cells are preferably in the range of from about 0.03 to about 0.75 mm.

The invention is particularly useful for thermoplastic polymers, where the effective temperature of the transition of the foam from a highly elastic state to glassy is from about 75 ° C to about 140 ° C. The actual temperature of the glassy state of the foam, compared with the transition temperature from the highly elastic state to the glassy, natural thermoplastic polymer, is the temperature of the transition from the highly elastic state to the glassy state of the foam in an energy absorbing structural element that was once taken into account, for example, plasticizing the effect that a blowing agent may have at the transition temperature of the polymer foam into a glassy state e. The invention is especially useful because it allows foams with a low glass transition temperature, the strength of which, otherwise, can lead to swelling or explosion upon heating, can be dimensionally stable at high temperatures. Preferably, the effective glass transition temperature is from at least about 80 ° C, more preferably from at least about 85 ° C, even more preferably from at least about 90 ° C, and most preferably from at least about 95 ° C to, preferably, not more than about 135 ° C, more preferably to not more than about 130 ° C, even more preferably to not more than about 125 ° C and most preferably to not more than about 120 ° C.

The actual temperature of the glassy state of the foam can be determined by ASTM D4065-01 - a method for determining dynamic, mechanical properties. Modules of elasticity and ductility of the foam are measured by dynamic, thermomechanical analyzers, such as:

Rheometric Scientific RDA III Dynamic Mechanical Analyzer or Rheometrix Dynamic Mechanical Thermal Analyzer RSA II, made by Rheometric Scientific Inc., TA Instruments Group, New Castle, DE. These modules are a function of temperature and change rapidly over a specific temperature range. Areas of rapid change of modules are usually referred to as transition areas, and the glazing temperature is determined in accordance with the standard.

To quickly achieve dimensional stability, it is necessary that the average gas pressure in the closed cells be from about 0.5 to about 1.4 atmospheres. When such gas pressure was present in the foam of an energy absorbing structural member, it was found that the largest linear dimensional change in total was less than about 5%, making it useful for energy absorbing structural members. It is understood that the aforementioned gas pressure is the gas pressure that was measured by the previously described method and is given to represent the average pressure in closed cells under ambient conditions. The most desirable average gas pressure in the cells depends on many factors, such as: polymer features, foam structure, blowing agent, effective glass transition temperature, and can be easily determined using one of the simple methods currently known without inappropriate experiments with this foam. However, it is desirable that the gas pressure in the cells is less than atmospheric pressure in order to minimize the possibility of foam swelling, which will lead to the displacement of other structural elements of the vehicle, for example, creaking or foam displacement in the structural element. Preferably, the average gas pressure in the cells is less than 1.2, more preferably less than about 1.1 atmospheres, even more preferably the pressure is not more than about 1.0 atmospheres, even more preferably not more than about 0.99 and most preferably not more than about 0.95 atmospheres.

Similarly, the average gas pressure is preferably at least about 0.55 atmospheres, more preferably at least 0.6 atmospheres, and most preferably at least about 0.7 atmospheres to protect against, for example, too much restriction on a sunny day in a car . The average gas pressure in the closed cells can be calculated using the gas diffusion rate by estimating the gas content in the cellular material at different times if the initial time when the foam was made is known (e.g. ASTM D7132-05). However, since the initial production time of the foam is not always known, the following empirical methods are used here. To determine the average internal gas pressure in the closed cells of the foam of an energy-absorbing structural member, at least 3 pieces of cube-shaped foam with sides approximately 50 mm in length are individually placed in a thermostat at 85 ° C in vacuum (1 torr or less), at 0.5 atmosphere and at ambient pressure (1 atmosphere) for 12 hours. The pressure was set as quickly as possible after the cubes were placed in a thermostat. After 12 hours, the thermostat was cooled to room temperature without changing the pressure in the thermostat. After the cube had cooled, it was removed and the maximum change in size was determined in each mutually perpendicular direction of the cube. Then, the maximum linear dimensional change was determined using the initial dimensions, the pressure dependence is shown, and the dependence is plotted in a straight line using a linear regression analysis of the average internal pressure in the cell, which is the pressure where the resulting line has zero dimensional changes (see Fig. 2) .

The foam of an energy-absorbing structural member is invariably produced using a physical or chemical blowing agent and, as usual, has some residue of the blowing agent in the cells or it dissolves in the polymer itself. The foam can have any suitable blowing agent, such as a volatile aliphatic or cyclic hydrocarbon, chlorine-containing hydrocarbon, fluorine-containing hydrocarbon, chlorine-fluorine-containing hydrocarbon, alcohol, ketone, ether, gas present in the atmosphere (oxygen, nitrogen, carbon dioxide, hydrogen, helium and something similar) or combinations of this.

Examples of volatile hydrocarbons include: ethane, ethylene, propane, propylene, butane, butylene, isobutane, pentane, cyclopentane, isopentane, hexane, heptane, or mixtures thereof. Examples of chlorine-containing hydrocarbons, fluorine-containing hydrocarbons, chlorine-fluorine-containing hydrocarbons include: methyl chloride, dichlorodifluoromethane, octafluorocyclobutane, chlorodifluoromethane, 1,2, -dichlorotetrafluoroethane, 1,1, -dichlorotetrafluoroethane, pentafluoroetho-ethane, 2-2-chloro chloro-1,1,1-trifluoroethane, 1,1,1,2-tetrafluoroethane, 1,1,1-trifluoroethane, 1,1,1-trifluoropropane, trichlorotrifluoroethane, difluoromethane, 2-chloro-1,1,1, 2-tetrafluoroethane, 2,2-difluoropropane, ethyl fluoride, 1,1-difluoroethane, 1,1,2,2-tetrafluoroethane, pentafluoroethane, perfluoroethane, 2,2-difluoropropane, 1 1,1-trifluoropropane and 1,1,1,2,3,3,3-heptafluoropropane 1,1,1,3,3-pentafluoropropane and 1,1,1,3,3-pentafluorobutane ethyl chloride or a mixture of these substances.

Examples of aliphatic alcohols having from one to five carbons (C1-C5) include methanol, ethanol, n-propanol, isopropanol, or a mixture of these substances; examples of carbonyl-containing compounds include: acetone, 2-butanone, acetic aldehyde or mixtures thereof; examples of ether-containing compounds include dimethyl ether, diethyl ether, methyl ethyl ether or mixtures thereof. Examples of other suitable chemical blowing agents include azodicarbonamide, azodiisobutyronitrile, benzenesulfohydrazine, 4,4-hydroxybenzene sulfonyl hemi-carbazide, p-toluene sulfonyl hemi-carbazide, barium azodicarboxylate, N, N'-dimethyl-dinazide tri-dinazole tri-dinazide tri-dinazole tri-dinazole dinitrosine dinazole tri-dinazole tri-dinazide dinitrosin triazole. .

Clearly for polystyrene and polystyrene copolymers, chlorine fluorine derivatives of hydrocarbons are commonly used as blowing agents. This leads to plasticization of the polymer and leads to a lower effective glass transition temperature, which may cause the foam to be unable to be dimensionally stable. This also led, due to their slow diffusion rate, to the formation of foam, where the average gas pressure is more than 1 atmosphere even after the foam has been aged for a long period of time. Therefore, it is preferable that at least one blowing agent or one component of a mixture of blowing agents has a significantly higher diffusion rate through the foam than air to facilitate the production of foam having the aforementioned average gas pressure. Significantly faster in this context means that the speed of diffusion of the blowing agent is not less than about 2 times greater than the speed of diffusion of air. Air diffusion is taken as the average diffusion rate of oxygen and nitrogen, suspended in the presence of each of them in the air. Preferably, the diffusion rate of the blowing agent is not less than about 3 times faster, more preferably not less than 4 times, even more preferably not less than 5 times, and most preferably not less than 10 times, than the air diffusion rate.

Since, for example, in connection with environmental concerns, it is particularly desirable to carry out the invention when the amorphous thermoplastic polymer is a polystyrene or polystyrene copolymer and the blowing agent includes carbon dioxide, water, or a combination thereof. Preferably for this embodiment, the blowing agent is carbon dioxide.

Formation of a structural element absorbing energy

An element of the structure absorbing energy can be made as follows. An amorphous thermoplastic polymer and a blowing agent are mixed together. Any convenient method of mixing the polymer and the blowing agent can be used such as, for example, those known in the art. For example, a blowing agent can be injected into a polymer that has been heated in an extruder as described in US Pat. No. 3,231,524; 3,482,006; 4,420,448 and 5,340,844 or a blowing agent may be added to the polymer granules, usually under pressure, as described by US Pat. No. 4,485,193 and each of the US patents. This patent refers to col.3, lines 6-13.

After the polymer and the blowing agent are mixed, the polymer and the blowing agent are placed in a template that can have a final or intermediate shape and can be made by any suitable method such as is known in the art (for example, stamping foam beams and foam beads). For example, when extrusion is used, the foam bar can be of any shape, and this bar can later be cut into more complex final shapes, or the foam slab can be cut into pieces of another useful shape, which then, after hot molding, acquire the desired final shape. The use of hot forming can also be beneficial in this process, it can create a more impermeable coating that allows you to maintain the desired gas pressure in this structural element, absorbing energy.

Such hot molding, which is well known in the art and described, for example, by US Pat. Nos. 2,899,708; 3,334,169; 3,484,510; 3923948 and 4359160, can be done at any time after receiving the molded foam, but it is preferable to do this after the molded foam has an individual gas pressure (for example, after processing). The average gas pressure in the closed cells during hot forming may be any as previously described, but lower pressure is preferable because compaction of the foam during hot forming can increase pressure. Visually, the foam gas pressure is from not more than about 1 atmosphere, preferably from not more than about 0.95 atmospheres, 0.9, more preferably from not more than about 0.85, and most preferably from not more than about 0.8 to not less than about 0, 5.

To repeat, the molded foam is processed to obtain the aforementioned average gas pressure in the closed cells of the foam of the energy absorbing structural member. The treatment can be of any duration during aging, sufficient to prepare the foam with the proper average gas pressure. The amount of time that is sufficient depends on many factors, such as the polymer of the foam, the size of the part, the blowing agent used, and the aging atmosphere. A simple skill in the art can determine an adequate time without undue experimentation. Typically, time can range from 1 day to 1 year or more.

In the preferred method, an extruded foam bar is formed, which is then aligned to create open cells on the surface of the extruded foam bar and / or perforated to create a foam having a gas diffusion distance as previously described. Preferably, at least both the top and bottom of the foam bar are aligned (i.e., significant surfaces of the bar, or for example, a 4 '× 8' surface, of a bar with dimensions of 4 '× 8' × 1 '). This was surprisingly found to allow a reduction in processing time under ambient conditions, especially when the blowing agent included carbon dioxide or carbon dioxide and water. When perforating a foam bar, the holes may extend through the thickness of the bar or form blind cavities. Holes can be made in the same manner as described in US Pat. No. 5,424,016 to release trapped, combustible hydrocarbon gases (e.g., isobutane and pentane) from the foam bar.

In addition, if necessary, the treatment may include a temperature higher than normal but lower than the temperature at which the foam can warp, which is easily determined depending on the use of a particular polymer. The treatment may also include the use of various atmospheres, for example, the atmosphere may be dry air if water is used as a blowing agent. The pressure of the atmosphere surrounding the molded foam can also be lower (vacuum) or higher than atmospheric pressure, as long as the vacuum or increased pressure is not so great that the foam warps. Preferably, for convenience, the pressure is ambient pressure and the atmosphere is air.

The processed molded foam may also have a decorative coating or impermeable membrane applied to part of the surface or to the entire surface of the foam. The impermeable membrane may be of any material that restricts or stops the migration of gases into or from the foam. Such films may be applied by any suitable method, such as those known in the art (for example, sputtering, chemical vacuum deposition, adhesive films, films or sheets using adhesive or thermal cure). Examples of impermeable membranes include metal films (e.g. silver, aluminum, iron-based films such as steel films) and plastic films such as polyethylene (PET) film, polyamide films, or combinations thereof.

In conclusion, in order to make the structural element absorbing energy, the processed, molded foam is attached to the structural part. The processed molded foam can be foamed directly, for example, in the cavity of a structural part when it is used, for example, expandable foam granules in a helmet shell or in a door panel. The cavity can be integrated into the structural element to facilitate the fixing of the foam. The foam can also be attached to the structural element by any suitable method, such as those known in the art, including, for example, mechanical (for example, fasteners) or chemical (for example, gluing and heating the structural part to a sufficient temperature at which the foam is attached to the structural part when the foam is brought into contact with the structural element and is attached, by applying a solvent, to the surface of the foam, bringing it into contact structural parts).

Examples

Example 1

A bar measuring 100 mm × 600 mm × 1200 mm (thickness × width × length) FLOORMATE ^™ 200-A (extruded gas-filled polystyrene available from The Dow Chemical Company, Midland, MI) was stored for about a year under ambient conditions, after which how was produced. The foam had a density of about 35 kg / m ³ and the foam was a closed-cell foam, which basically means that at least 90% of the cells are closed. The blowing agent was carbon dioxide, n-pentane and isopentane. Then a 50 mm cube was cut with a band saw in the cross-sectional area of the bar. After the dimensions of the cube were measured with a caliper, the sample was placed in a convection oven for twenty-four hours at 85 ° C. The cube after cooling was measured and the percent change in each direction was set as shown in Table 1. The gas pressure in the closed cells was measured as described here and presented in Table 2.

Example 2

A bar measuring 100 mm × 600 mm × 2200 mm (thickness × width × length) of extruded gas-filled polystyrene was produced on large-scale production equipment using CO ₂ as a blowing agent in the same way as described in comparative example 1 of US patent No. 5340844. The foam had a density of about 35 kg / m ³ and at least 90% of the cells were closed cells. After the bar was extruded, it was perforated using a 2 mm spoke through the entire thickness of the bar. The perforation intervals were of the order of 10 mm in width and 20 mm in length. The bar was stored for approximately 19 days prior to perforation and 13 days under ambient conditions after perforation. Then, a 50 mm cube was cut in the cross-sectional area of the bar, measured and checked as in Example 1, with the results shown in Table 2. The cube, after heating to 85 ° C for 24 hours, is shown in FIG. 1 in the right photo in comparison with the cube of comparative example 1, which is presented in the left photo.

Example 3

A 200 mm × 600 mm × 2500 mm bar (thickness × width × length) STYROFOAM ^™ FB-X (extruded gas-filled polystyrene available from The Dow Chemical Company, Midland, MI) was stored for approximately 8 months under ambient conditions how was produced. The foam was produced using an HFC-134a blowing agent. The foam had a density of about 36.5 kg / m ³ and was closed cell foam. Then a 50mm bar was cut out in the cross-sectional area of the bar, measured and checked as in Example 1, with the results presented in Table 2.

Example 4

A bar measuring 50 mm × 600 mm × 2200 mm (thickness × width × length) of extruded gas-filled polystyrene was produced on large-scale production equipment using CO ₂ as a blowing agent in the same way as described in comparative example 1 of US patent No. 5340844, but with slightly elevated mold temperature to obtain enlarged open cells of this foam. The foam had a density of about 35.5 kg / m ³ and about 50% of the open cells. The bar was stored for 40 days under ambient conditions. Then, a 50 mm bar was cut in the cross-sectional area of the bar, measured and checked as in Example 1, except that the time at temperature was 13 days, with the results shown in Table 2.

Example 5

Section 89 mm × 356 mm × 610 mm (thickness × width × length) of a STYROFOAM * art board plank (extruded gas-filled polystyrene available from The Dow Chemical Company, Midland, MI, * Trademark of the Dow Chemical Company) was perforated as described in example 2, except that the perforation gaps were about 15 mm wide. This foam was made using a blowing agent HCFC-142b. The foam had a density of about 31.2 kg / m ³ and was closed cell foam. After perforation, the bar was stored under ambient conditions for approximately 138 days. Then a 50 mm bar was cut in the cross-sectional area of the bar, measured and checked, as in Example 1, with the results presented in Table 2. Even though this foam did not have a particularly low pressure in the cell, it had acceptable dimensional stability, which applied to at least part of the perforation of the foam, and the aging time after perforating the foam gave a smooth line in the same way as shown in Example 2 of FIG. 2.

Comparative Example 1

A bar measuring 100 mm × 600 mm × 2200 mm (thickness × width × length) of extruded gas-filled polystyrene was produced in the same manner as in Example 2, except that the bar was not perforated and stored under ambient conditions for approximately 31 days. Then, a 50 mm bar was cut in the cross-sectional area of the bar, measured and checked, as in Example 1, with the results shown in Table 2. The cube, after heating to 85 ° C for 24 hours, is shown in FIG. 1, in the left photo, in comparison with the cube of example 2, which is presented in the right photo.

From this comparison it is clear that the use of perforation favorably influences the necessary internal pressure in the cell in this invention.

Reference Example 2

A FOAMULAR ^™ 600 sample having dimensions of 38 mm × 38 mm × 37 mm (extruded gas-filled polystyrene available from Owens Corning, Toledo, Ohio) was purchased and stored for approximately 441 days under ambient conditions. The blowing agent was HCFC-142b. The foam had a density of about 37 kg / m ³ and was closed cell foam. Then this cube was measured and tested, as in example 1, with the results presented in Table 2.

Reference Example 3

A bar measuring 75 mm × 1219 mm × 2438 mm (thickness × width × length) STYROFOAM FREEZERMATE ^™ (extruded gas-filled polystyrene available from The Dow Chemical Company) was produced and stored for approximately 398 days under ambient conditions after being produced. The blowing agent was HCFC-142b. The foam had a density of about 30.2 kg / m ³ and was closed cell foam. Then a 50 mm bar was cut in the cross-sectional area of the bar, measured and checked as in Example 1, with the results presented in Table 2.

Reference Example 4

A block of 89 mm × 1219 mm × 2438 mm (thickness × width × length) STYROFOAM * art board plank (extruded gas-filled polystyrene available from The Dow Chemical Company, Midland, MI, * Trademark of the Dow Chemical Company) was produced and stored for at least 138 days, under ambient conditions, after being produced, the storage time was the same as the total storage time in example 5. The blowing agent was HCFC-142b. The foam had a density of about 32.2 kg / m ³ and about 90% of the cells were closed cells. Then a 50 mm bar was cut in the cross-sectional area of the bar, measured and checked, as in example 1, with the results presented in Table 2.

Based on the presented data, it is preferable to use carbon dioxide as a blowing agent with or without other substance in the manufacture of the foam according to this invention, since this invention requires a very shortened aging time in order to obtain the necessary pressure in the cell according to this invention. Surprisingly, the use of CO ₂ as a blowing agent, as can be seen from the graph shown in FIG. 2 (examples 1 and 2), also shows a reduced angle of inclination of the dimensional change with pressure, thus making it less capable of excessive deformation at pressures that can possibly be obtained during operation. Similarly, the data show that the use of perforation also helps to achieve the required pressure in the cell (see example 2 and comparative example 1) and to decrease the slope of the dimensional change with pressure (see Fig. 2). In conclusion, the foam with substantially open cells shows the smallest angle of inclination (Fig. 2, example 4).

Claims (43)

1. An element of an energy-absorbing structure, comprising an amorphous thermoplastic cellular polymer, which is a polystyrene polymer or a polystyrene copolymer, in contact with a structural element in which at least about 50% of the cells of the amorphous cellular polymer are closed cells and have an average gas pressure that is between from about 0.5 atm to about 1.4 atm at ambient temperature. 2. The energy-absorbing structure of claim 1, wherein the structural element is a helmet shell, a car door panel, a car door pillar, a car roof, or a car instrument panel. 3. The energy-absorbing member of claim 2, wherein the structural member is a car door panel, a car door pillar, or a car roof. 4. The energy-absorbing member of claim 1, wherein the amorphous thermoplastic cellular polymer is a polystyrene polymer. 5. The energy-absorbing member of claim 4, wherein the polystyrene polymer is polystyrene. 6. The energy absorbing element of claim 1, wherein the amorphous thermoplastic cellular polymer is a polystyrene copolymer. 7. The energy absorbing structure of claim 6, wherein the polystyrene copolymer is a copolymer of styrene monomer and comonomer selected from the group consisting of acrylonitrile, poly-2,6-dimethyl-1,4-phenylene ether, methyl acrylate, methacrylonitrile, maleimide , acrylic acid, methacrylic acid, maleic anhydride, itaconic anhydride, and combinations thereof. 8. The energy absorbing element of claim 7, wherein the comonomer is acrylonitrile. 9. The energy absorbing structure of claim 8, wherein the acrylonitrile is present in an amount of from about 1% to about 35% by weight of an amorphous thermoplastic cellular polymer. 10. The energy absorbing structure of claim 9, wherein the acrylonitrile is present in an amount of not more than about 15%. 11. The energy absorbing structure of claim 10, wherein the acrylonitrile is present in an amount of not more than about 20%. 12. The energy absorbing element of claim 1, wherein the amorphous thermoplastic cellular polymer contains a blowing agent residue. 13. The energy absorbing member of claim 12, wherein the blowing agent includes a volatile aliphatic or cyclic hydrocarbon, alcohol, ketone, ether, carbon dioxide, water, or a combination of these. 14. The energy absorbing structure of claim 13, wherein the blowing agent includes ethane, ethylene, propane, propylene, butane, isobutane, butylenes, isobutene, pentane, isopentane, cyclopentane, hexane, heptane, ethanol, propanol, isopropanol, butanol, acetone, dimethyl ether, carbon dioxide, water, or a combination thereof. 15. The energy absorbing structure of claim 12, wherein the blowing agent consists of carbon dioxide, water, or a combination thereof. 16. The energy absorbing structure of claim 13, wherein the at least one blowing agent has a diffusion rate through the amorphous thermoplastic cellular polymer that is greater than the diffusion rate of air through said polymer. 17. The energy absorbing structure of claim 16, wherein all blowing agents have a diffusion rate through the amorphous thermoplastic cellular polymer that is greater than the rate of diffusion of air through said polymer. 18. The energy absorbing member of claim 12, wherein the blowing agent is carbon dioxide, water, or a combination thereof. 19. The energy-absorbing member of claim 1, wherein the amorphous thermoplastic cellular polymer has an effective glass transition temperature of from about 85 ° C to about 135 ° C. 20. The energy-absorbing member of claim 19, wherein the amorphous thermoplastic cellular polymer has an effective glass transition temperature of from about 90 ° C to about 125 ° C. 21. The energy-absorbing structure of claim 20, wherein the amorphous thermoplastic cellular polymer has an effective glass transition temperature of not more than about 120 ° C. 22. The energy-absorbing member of claim 1, wherein at least about 70% of the cells of the amorphous cellular polymer are closed cells. 23. The energy absorbing structure of claim 22, wherein at least about 90% of the cells of the amorphous cellular polymer are closed cells. 24. The energy absorbing element of claim 1, wherein the maximum diffusion length of the closed cells into the atmosphere surrounding the amorphous thermoplastic cellular polymer is not more than about 20 mm. 25. The energy absorbing structure according to claim 24, wherein the maximum diffusion length is not more than about 10 mm. 26. The energy-absorbing member of claim 1, wherein the average gas pressure in the closed cells is less than 1.2 atm. 27. The energy-absorbing structure according to claim 26, wherein the average gas pressure in the closed cells is not less than about 0.6 atm. 28. The energy-absorbing element of claim 27, wherein the average gas pressure in the closed cells is at least about 0.7 atm. 29. The energy-absorbing structure of claim 28, wherein the average gas pressure in the closed cells is at least about 0.75 atm. 30. An energy absorbing element according to any one of claims 26-29, wherein the average gas pressure in closed cells is not more than 0.99 atm. 31. An energy absorbing structure according to claim 30, wherein the average gas pressure in the closed cells is not more than 0.95 atm. 32. A method of manufacturing an element of an energy-absorbing structure comprising:
(a) mixing an amorphous thermoplastic polymer, which is a polystyrene polymer or polystyrene copolymer, and a blowing agent,
(b) preparing a molded polymer foam from a mixture of a polymer that is a polystyrene polymer or a polystyrene copolymer and a blowing agent in which the foam has at least about 50% of the closed cells,
(C) processing the prepared molded foam so that the closed cells have a gas pressure of from about 0.5 to about 1.4 atmospheres to obtain the prepared processed molded foam, and
(d) attaching the prepared processed molded foam to a structural member to obtain an energy absorbing structural member. 33. The method according to p, in which the blowing agent is carbon dioxide, water, or a combination thereof. 34. The method according to p, in which the blowing agent is carbon dioxide. 35. The method according to p, in which the formation is the extrusion of the mixture prepared in operation (a), processing by leveling at least one surface of the molded polymer foam and keeping the aligned molded polymer foam for sufficient time to obtain a processed molded polymer foam. 36. The method according to clause 35, in which the molded polymer foam further changes shape by thermal molding. 37. The method according to any of paragraphs.32-36, in which the processing includes perforation of the molded polymer foam. 38. The method according to clause 36, in which the molded polymer foam is perforated before thermal molding. 39. The method according to § 38, in which the molded polymer foam is perforated after thermal molding. 40. The method according to p, in which the molded polymer foam is formed by cutting with wire. 41. The method according to p, in which the processing includes perforation of the molded polymer foam. 42. The method according to paragraph 41, in which the perforation of the molded polymer foam occurs before cutting with wire. 43. The method according to p, in which the perforation of the molded polymer foam occurs after cutting with wire.

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